This invention relates to a process for the production of a malolactic ferment, to the ferment thus obtained and to its use in the production of a wine.
There are various processes for deacidifying wine by malolactic fermentation during which malolactic bacteria, more particularly Leuconostoc oenos and certain lactobacilli, convert the malic acid present in the wine into lactic acid.
U.S. Pat. No. 4,380,552, for example, proposes deacidifying a wine by passing it through a bed of gel beads containing viable cells of Leuconostoc oenos . However, it is not certain that this process is any better than direct inoculation of the wine with this bacterium.
In European Patent Application Publication No. 327 380, wine is subjected to controlled malolactic fermentation by passage through a vessel containing at least 10.sup.8 cells of malolactic bacteria per ml and delimited upstream and downstream by filters which retain the bacteria. The same batch of bacteria could be used for a relatively long time in continuous operation or for up to 5 or 6 months by carrying out fermentation in batches. However, both the process and the equipment used appear relatively complicated.
U.S. Pat. No. 4,562,077 proposes reducing the malic acid content of a wine by converting this acid into lactic acid using frozen or freeze-dried ferments containing strains of Leuconostoc oenos selected for their good activity in a quantity of 10.sup.8 to 10.sup.13 cells/ml. However, the proposed ferments have to be specially activated before the wine can be inoculated with them.
U.S. Pat. No. 4,547,373 proposes strains of Leuconostoc oenos capable of achieving relatively rapid malolactic fermentation, namely in about 50 to 100 d, for example at a relatively low temperature of approximately 16.degree. to 18.degree. C. and at a relatively low pH value of about 3.1 to 3.2.
In addition, there are commercially available malolactic ferments intended for use in traditional vinification when it is desired to exercise better control over the malolactic fermentation of a must or a wine rich in malic acid. However, almost all these commercial ferments have to be reactivated before use, for example over a period of two days on a particular medium, which complicates the task of the cellarman.
There are also various processes for making so-called light wines, i.e. wines of which the alcohol content is substantially reduced in relation to that of a so-called normal wine which has an alcohol content of approximately 8.5 to 16% by volume (8.5.degree. to 16.degree. alcohol).
U.S. Pat. No. 4,626,437, for example, describes a process for making a light wine in which a normal wine is subjected to an evaporation process to remove alcohol and aromatic constituents, leaving a condensate which is then subjected to fractional distillation to remove an aromatic fraction and the aromatic fraction thus obtained is returned to the wine reduced in alcohol and aromatic constituents. Unfortunately, a light wine made in this way can still have a substantially modified flavour in relation to that of the starting wine.
U.S. Pat. No. 4,902,518 describes a process for making a light wine in which grape juice is separated into a fraction rich in sugar and a fraction poor in sugar, an aromatic fraction is recovered from the fraction rich in sugar and is added to the fraction poor in sugar which is then subjected to traditional fermentation. A light wine made in this way can differ considerably in its flavour from a wine obtained by traditional fermentation of the starting grape juice.
Since the flavour of a wine is significantly influenced or even strengthened by malolactic fermentation during or after alcoholic fermentation, it could be of advantage to subject light wines of the type in question to malolactic fermentation during or after their production. However, this would presuppose control of the malolactic fermentation process.
Accordingly, there is a need for a reliable and effective malolactic ferment which would be capable of initiating and then rapidly completing malolactic fermentation on direct inoculation into a normal or light wine.